A new study finds that the fear of spiders and snakes actually stems from our ancestors. We likely developed these fears as a result of our ancestors' coexistence with them for millions of years.

Fear Of Spiders And Snakes

Over a third of both the children and adult population have a strong dislike or fear of spiders, despite having only a 5 percent prevalence rate of related clinical fear or phobia. Somehow it makes sense. After all, earlier this year, scientists found that the world's spiders could eat every human in a single year and still crave for more.

That unsettling finding aside, this fear is prevalent even in countries where people do not often have snake or spider encounters. They're not much of a threat today, and yet people still tend to fear them. As it turns out, humans today don't even have to have negative experiences with the creatures to fear them because they are likely embedded in us thanks to our ancestors' coexistence with them for 40 to 60 million years.

Spiders And Flowers, Snakes And Fish

In order to test the hypothesis, researchers at the Max Planck Institute for Human Cognitive and Brain Sciences (MPI CBS) in Sweden measured the pupil dilation of 6-month-old infants when they were shown photos of either spiders or flowers, and snakes or fish. Dilation reactions to spiders and flowers were compared, and so were dilation reactions to snakes and fish. Short breaks were made to prevent fatigue.

Results showed increased pupil dilation when the infants were presented with spider pictures compared to the non-threatening stimuli of the flower photos. Further, the participants also looked at spider photos for a longer amount of time. This suggests stimuli arousal and fear-associations to spiders even at such a tender age. However, the snake-fish experiment rendered minimal differences in pupil dilation, suggesting perhaps that the infant merely have an eye for living things.

To rule this possibility out, researchers conducted another experiment, this time showing one group of infants only snake photos and another only fish photos. The results indicate increased pupil dilation among the infants shown snake photos compared to the fish-only group.

Ancestral Threat

Results of the two experiments suggest that our ancestors' fear of threatening stimuli such as spiders and snakes seem to have been carried over to modern humans. The threat that our ancestors experienced already induces stress responses to modern humans even at the very young age of six months.

"The reaction which is induced by animal groups feared from birth could have been embedded in the brain for an evolutionarily long time," said Stefanie Hoehl of MPI CBS and the University of Vienna, lead investigator of the study. Pertaining to more modern threats such as knives and syringes, Hoehl states that they have not been around long enough to establish threat responses from birth.

The study is published in Frontiers In Psychology.

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